Interference control in a wireless communication system

ABSTRACT

For interference control, a sector m estimates interference observed from terminals in neighbor sectors and obtains an interference estimate. Sector m may generate an over-the-air (OTA) other-sector interference (OSI) report and/or an inter-sector (IS) OSI report based on the interference estimate. Sector m may broadcast the OTA OSI report to the terminals in the neighbor sectors. These terminals may adjust their transmit powers based on the OTA OSI report. Sector m may send the IS OSI report to the neighbor sectors, receive IS OSI reports from the neighbor sectors, and regulate data transmissions for terminals in sector m based on the received IS OSI reports. Sector m may control admission of terminals to sector m, de-assign admitted terminals, schedule terminals in sector m in a manner to reduce interference to the neighbor sectors, and/or assign the terminals in sector m with traffic channels that cause less interference to the neighbor sectors.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/158,584 filed Jun. 21, 2005, which claims priority to U.S.Provisional Patent Application Ser. No. 60/662,176, filed Mar. 15, 2005.The aforementioned applications are incorporated herein by reference intheir entirety.

BACKGROUND

I. Field

The present disclosure relates generally to communication, and morespecifically to interference control in a wireless communication system.

II. Background

A wireless multiple-access communication system can concurrentlycommunicate with multiple terminals on the forward and reverse links.The forward link (or downlink) refers to the communication link from thebase stations to the terminals, and the reverse link (or uplink) refersto the communication link from the terminals to the base stations.Multiple terminals may simultaneously transmit data on the reverse linkand/or receive data on the forward link. This is often achieved bymultiplexing the transmissions on each link to be orthogonal to oneanother in time, frequency and/or code domain.

On the reverse link, the transmissions from terminals communicating withdifferent base stations are typically not orthogonal to one another.Consequently, each terminal may cause interference to other terminalscommunicating with nearby base stations and may also receiveinterference from these other terminals. The performance of eachterminal is degraded by the interference from the other terminalscommunicating with other base stations.

There is therefore a need in the art for techniques to mitigateinterference in a wireless communication system.

SUMMARY

Techniques for controlling interference observed by each sector fromneighbor sectors in a wireless communication system are describedherein. The term “sector” can refer to a base station or the coveragearea of the base station. A sector m estimates interference observedfrom terminals in neighbor sectors and obtains an interference estimate.For user-based interference control, sector m generates an over-the-air(OTA) other-sector interference (OSI) report based on the interferenceestimate and broadcasts the OTA OSI report to the terminals in theneighbor sectors. These terminals may autonomously adjust their transmitpowers based on the OTA OSI report from sector m, if necessary, toreduce the amount of interference observed by sector m. The OTA OSIreport may indicate one of multiple possible levels of interferenceobserved by sector m. The terminals in the neighbor sectors may adjusttheir transmit powers by different amounts and/or at different ratesdepending on the interference level observed by sector m.

For network-based interference control, sector m generates aninter-sector (IS) OSI report based on the interference estimate andsends the IS OSI report to the neighbor sectors. The IS OSI report maybe the same as the OTA OSI report or may be more comprehensive. Sector malso receives IS OSI reports from the neighbor sectors and regulatesdata transmissions for the terminals in sector m based on the receivedIS OSI reports. Sector m may regulate data transmissions by (1)controlling admission of new terminals to sector m, (2) de-assigningterminals that have already been admitted, (3) scheduling the terminalsin sector m in a manner to reduce interference to the neighbor sectors,and/or (4) assigning the terminals in sector m with traffic channelsthat cause less interference to the neighbor sectors.

Various aspects and embodiments of the invention are described infurther detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and nature of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings in which like reference charactersidentify correspondingly throughout.

FIG. 1 shows a communication system with base stations and terminals.

FIG. 2 shows a process performed by one sector for interference control.

FIG. 3 shows a process performed by one terminal for interferencecontrol.

FIG. 4 shows a process for adjusting transmit power in a deterministicmanner.

FIG. 5 shows a process for adjusting transmit power in a probabilisticmanner.

FIG. 6 shows a power control mechanism suitable for interferencecontrol.

FIG. 7 shows a block diagram of a terminal and two base stations.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs.

FIG. 1 shows a wireless communication system 100 with multiple basestations 110 and multiple terminals 120. A base station is generally afixed station that communicates with the terminals and may also becalled an access point, a Node B, or some other terminology. Each basestation 110 provides communication coverage for a particular geographicarea 102. The term “cell” can refer to a base station and/or itscoverage area depending on the context in which the term is used. Toimprove system capacity, the base station coverage area may bepartitioned into multiple smaller areas, e.g., three smaller areas 104a, 104 b, and 104 c. Each smaller area is served by a respective basetransceiver subsystem (BTS). The term “sector” can refer to a BTS and/orits coverage area depending on the context in which the term is used.For a sectorized cell, the BTSs for all sectors of that cell aretypically co-located within the base station for the cell. A systemcontroller 130 couples to base stations 110 and provides coordinationand control for these base stations.

A terminal may be fixed or mobile and may also be called a mobilestation, a wireless device, a user equipment, or some other terminology.Each terminal may communicate with zero, one, or multiple base stationsat any given moment.

The interference control techniques described herein may be used for asystem with sectorized cells and a system with un-sectorized cells. Inthe following description, the term “sector” refers to (1) aconventional BTS and/or its coverage area for a system with sectorizedcells and (2) a conventional base station and/or its coverage area for asystem with un-sectorized cells. The terms “terminal” and “user” areused interchangeably, and the terms “sector” and “base station” are alsoused interchangeably. A serving base station/sector is a basestation/sector with which a terminal communicates. A neighbor basestation/sector is a base station/sector with which the terminal is notin communication.

The interference control techniques may also be used for variousmultiple-access communication systems. For example, these techniques maybe used for a code division multiple access (CDMA) system, a frequencydivision multiple access (FDMA) system, a time division multiple access(TDMA) system, an orthogonal frequency division multiple access (OFDMA)system, an interleaved (IFDMA) system, a localized FDMA (LFDMA) system,a spatial division multiple access (SDMA) system, a quasi-orthogonalmultiple-access system, and so on. IFDMA is also called distributedFDMA, and LFDMA is also called narrowband FDMA or classical FDMA. AnOFDMA system utilizes orthogonal frequency division multiplexing (OFDM).OFDM, IFDMA, and LFDMA effectively partition the overall systembandwidth into multiple (K) orthogonal frequency subbands. Thesesubbands are also called tones, subcarriers, bins, and so on. Eachsubband is associated with a respective subcarrier that may be modulatedwith data. OFDM transmits modulation symbols in the frequency domain onall or a subset of the K subbands. IFDMA transmits modulation symbols inthe time domain on subbands that are uniformly distributed across the Ksubbands. LFDMA transmits modulation symbols in the time domain andtypically on adjacent subbands.

As shown in FIG. 1 each sector may receive “desired” transmissions fromterminals within the sector as well as “interfering” transmissions fromterminals in other sectors. The total interference observed at eachsector is composed of (1) intra-sector interference from terminalswithin the same sector and (2) inter-sector interference from terminalsin other sectors. The inter-sector interference, which is also calledother sector interference (OSI), results from the transmissions in eachsector not being orthogonal to the transmissions in the other sectors.The inter-sector interference and intra-sector interference have a largeimpact on performance and may be mitigated as described below.

Inter-sector interference may be controlled using various mechanismssuch as user-based interference control and network-based interferencecontrol. For user-based interference control, the terminals are informedof the inter-sector interference observed by the neighbor sectors andadjust their transmit powers accordingly so that the inter-sectorinterference is maintained within acceptable levels. For network-basedinterference control, each sector is informed of the inter-sectorinterference observed by the neighbor sectors and regulates datatransmissions for its terminals such that the inter-sector interferenceis maintained within acceptable levels. The system may utilize onlyuser-based interference control, or only network-based interferencecontrol, or both. Each interference control mechanism may be implementedin various manners, as described below.

FIG. 2 shows a process 200 performed by one sector m for inter-sectorinterference control. Sector m estimates interference observed fromterminals in other sectors and obtains an interference estimate (block210).

For user-based interference control, sector m generates an over-the-air(OTA) OSI report based on the interference estimate (block 212). The OTAOSI report conveys the amount of inter-sector interference observed bysector m and may be given in various forms, as described below. Sector mbroadcasts the OTA OSI report to the terminals in the neighbor sectors(block 214). These terminals may adjust their transmit powers based onthe OTA OSI report from sector m, if necessary, to reduce the amount ofinter-sector interference observed by sector m.

For network-based interference control, sector m generates aninter-sector (IS) OSI report based on the interference estimate (block222). The IS OSI report and the OTA OSI report are two interferencereports that may have the same or different formats. For example, the ISOSI report may be the same as the OTA OSI report. Alternatively, sectorm may broadcast a simple OTA OSI report to the terminals in the neighborsectors and may send a more comprehensive IS OSI report to the neighborsectors. Sector m may send the IS OSI report to the neighbor sectorsperiodically or only if sector m observes excessive interference (block224). Sector m also receives IS OSI reports from the neighbor sectors(block 226). The rate at which the IS OSI reports are exchanged amongthe sectors may be the same or different from the rate at which the OTAOSI reports are broadcast to the terminals. Sector m regulates datatransmissions for terminals in sector m based on the IS OSI reportsreceived from the neighbor sectors (block 228). The blocks in FIG. 2 aredescribed in further detail below.

Sector m may estimate the inter-sector interference in various manners.For a system utilizing orthogonal multiplexing, one terminal maytransmit data or pilot on each subband in each symbol period. A pilot isa transmission of symbols that are known a priori by both a transmitterand a receiver. A data symbol is a modulation symbol for data, a pilotsymbol is a modulation symbol for pilot, and a modulation symbol is acomplex value for a point in a signal constellation, e.g., for M-PSK,M-QAM, and so on.

Sector m may estimate the interference on a given subband k in a givensymbol period n based on a pilot received from a terminal u, as follows:

I _(m)(k,n)=|Ĥ _(m,u)(k,n)·P _(u)(k,n)−R _(m,u)(k,n)|²,  Eq (1)

where P_(u)(k,n) is a pilot symbol sent by terminal u on subband k insymbol period n;

Ĥ_(m,u)(k,n) is an estimate of the channel gain between sector m andterminal u;

R_(m,u)(k,n) is a received symbol obtained by sector m from terminal u;and

I_(in)(k,n) is an estimate of the interference observed by sector m.

The quantities in equation (1) are scalars.

Sector m may also estimate the interference based on data received fromterminal u, as follows:

I _(m)(k,n)=|Ĥ _(m,u)(k,n)·{circumflex over (D)} _(m,u)(k,n)−R_(m,u)(k,n)|²,  Eq (2)

where {circumflex over (D)}_(m,u)(k,n) is an estimate of a data symboltransmitted by terminal u on subband k in symbol period n. Sector m mayderive data symbol estimates {circumflex over (D)}_(m,u)(k,n) by (1)performing data detection on the received symbols R_(m,u)(k,n) with thechannel estimate Ĥ_(m,u)(k,n) to obtain detected symbols, (2) derivinghard-decisions based on the detected symbols, and (3) using thehard-decisions as the data symbol estimates. Alternatively, sector m mayderive the data symbol estimates by (1) performing data detection on thereceived symbols, (2) decoding the detected symbols to obtain decodeddata, and (3) re-encoding and symbol mapping the decoded data to obtainthe data symbol estimates.

Sector m may also perform joint channel and interference estimation toobtain both channel response estimates and interference estimates.

The interference estimate I_(m)(k,n) obtained from equation (1) or (2)includes both inter-sector interference and intra-sector interference.The intra-sector interference may be maintained within acceptable levelsvia power control, as described below, and may then be negligible incomparison to the inter-sector interference.

Sector m may average interference estimates across frequency, spatial,and/or time domains. For example, sector m may average the interferenceestimates across multiple receive antennas. Sector m may average theinterference estimates for all subbands using any one of the followingaveraging schemes:

$\begin{matrix}{{{I_{m}(n)} = {\frac{1}{K}{\sum\limits_{k = 1}^{K}\; {I_{m}( {k,n} )}}}},} & {{Eq}\mspace{14mu} (3)} \\{{{I_{m}(n)} = ( {\prod\limits_{k = 1}^{K}\; {I_{m}( {k,n} )}} )^{\frac{1}{K}}},{and}} & {{Eq}\mspace{14mu} (4)} \\{{{\log ( {1 + \frac{P_{nom}}{I_{m}(n)}} )} = {\frac{1}{K} \cdot {\sum\limits_{k = 1}^{K}\; {\log ( {1 + \frac{P_{nom}}{I_{m}( {k,n} )}} )}}}},} & {{Eq}\mspace{14mu} (5)}\end{matrix}$

where I_(m)(n) is the average interference power for sector m in symbolperiod n and P_(mon) denotes a nominal received power for each subband.I_(m)(k,n) and I_(m)(n) are in linear units in equations (3) through(5). Equation (3) is for arithmetic averaging, equation (4) is forgeometric averaging, and equation (5) is for SNR-based average. Witharithmetic averaging, a few large interference estimates can skew theaverage interference power. Geometric averaging and SNR-based averagingcan suppress large interference estimates for a few subbands.

Sector m may also filter the average interference power over multiplesymbol periods to improve the quality of the interference estimate. Thefiltering may be achieved with a finite impulse response (FIR) filter,an infinite impulses response (IIR) filter, or some other type offilter. Sector m obtains a measured interference I_(meas, m) for eachmeasurement period, which may span one or multiple symbol periods.

Sector m generates an OTA OSI report based on the measured interference.In an embodiment, the measured interference is quantized to apredetermined number of bits, which are included in the OTA OSI report.In another embodiment, the OTA OSI report includes a single bit thatindicates whether the measured interference is greater than or below aninterference threshold. In yet another embodiment, the OTA OSI reportincludes multiple bits that convey the measured interference relative tomultiple interference thresholds. For clarity, the following descriptionis for an embodiment in which the OTA OSI report conveys the measuredinterference relative to two interference thresholds.

In an embodiment, the OTA OSI report includes two binary OSI bits, whichare called OSI bit 1 and OSI bit 2. These OSI bits may be set asfollows:

$\begin{matrix}{{{OSI}\mspace{14mu} {bit}\; 1} = \{ \begin{matrix}{{{}_{}^{}{}_{}^{}},} & {{{{if}\mspace{14mu} I_{{meas},m}} \geq I_{nom\_ th}},} \\{{{}_{}^{}{}_{}^{}},} & {{{{if}\mspace{14mu} I_{{meas},m}} < I_{nom\_ th}},}\end{matrix} } & {{Eq}\mspace{14mu} ( {6a} )} \\{{{OSI}\mspace{14mu} {bit}\; 2} = \{ \begin{matrix}{{{}_{}^{}{}_{}^{}},} & {{{{if}\mspace{14mu} I_{{meas},m}} \geq I_{{high}{\_ th}}},} \\{{{}_{}^{}{}_{}^{}},} & {{{{if}\mspace{14mu} I_{{meas},m}} < I_{{high}{\_ th}}},}\end{matrix} } & {{Eq}\mspace{14mu} ( {6b} )}\end{matrix}$

where I_(nom) _(—) _(th) is a nominal interference threshold, I_(high)_(—) _(th) is a high interference threshold, and I_(high) _(—)_(th)>I_(nom) _(—) _(th). OSI bit 1 indicates whether the measuredinterference is above or below the nominal interference threshold. OSIbit 2 indicates whether the measured interference is above or below thehigh interference threshold. For this embodiment, sector m is deemed toobserve low interference if the measured interference is below highinterference if the measured interference is between I_(nom) _(—) _(th)and I_(high) _(—) _(th) and I_(nom) _(—) _(th), and excessiveinterference if the measured interference is greater than or equal toI_(high) _(—) _(th). OSI bit 2 may be used to indicate excessiveinterference being observed by the sector.

In another embodiment, the OTA OSI report includes a single OSI valuehaving three levels. The OSI value may be set as follows:

$\begin{matrix}{{{OSI}\mspace{14mu} {value}} = \{ \begin{matrix}{{{}_{}^{}{}_{}^{}},} & {{{{if}\mspace{14mu} I_{{meas},m}} \geq I_{{high}{\_ th}}},} \\{{{}_{}^{}{}_{}^{}},} & {{{{if}\mspace{14mu} I_{{high}{\_ th}}} > I_{{meas},m}},{\geq I_{nom\_ th}},} \\{{{}_{}^{}{}_{}^{}},} & {{{if}\mspace{14mu} I_{{meas},m}} < {I_{{nom}{\_ th}}.}}\end{matrix} } & {{Eq}\mspace{14mu} (7)}\end{matrix}$

The tri-level OSI value may be transmitted using a signal constellationhaving three signal points. For example, an OSI value of ‘0’ may be sentwith a symbol of 1+j0 or e^(j0), an OSI value of ‘1’ may be sent with asymbol of 0+j1 or e^(jπ/2), and an OSI value of ‘2’ may be sent with asymbol of −1+j0 or e^(jπ).

Alternatively, sector m may obtain a measured interference-over-thermal(IOT), which is a ratio of the total interference power observed bysector m to the thermal noise power. The total interference power may becomputed as described above. The thermal noise power may be estimated byturning off the transmitter and measuring the noise at the receiver. Aspecific operating point may be selected for the system. A higheroperating point allows the terminals to transmit at higher power levelson average. However, a high operating point has a negative impact onlink budget and may be undesirable. For a given maximum transmit powerand a given data rate, the tolerable maximum path loss decreases withincreasing IOT. A very high operating point is also undesirable sincethe system can become interference limited, which is a situation wherebyan increase in transmit power does not translate to an increase inreceived SNR. Furthermore, a very high operating point increases thelikelihood of system instability. In any case, sector m may set itstri-level OSI value as follows:

$\begin{matrix}{{{OSI}\mspace{14mu} {value}} = \{ \begin{matrix}{{{}_{}^{}{}_{}^{}},} & {{{{if}\mspace{14mu} {IOT}_{{meas},m}} \geq {IOT}_{{high}{\_ th}}},} \\{{{}_{}^{}{}_{}^{}},} & {{{{if}\mspace{14mu} {IOT}_{{high}{\_ th}}} > {IOT}_{{meas},m}},{\geq {IOT}_{nom\_ th}},} \\{{{}_{}^{}{}_{}^{}},} & {{{{if}\mspace{14mu} {IOT}_{{meas},m}} < {IOT}_{{nom}{\_ th}}},}\end{matrix} } & {{Eq}\mspace{14mu} (8)}\end{matrix}$

where IOT_(nom) _(—) _(th) is a nominal IOT threshold and IOT_(high)_(—) _(th) is a high IOT threshold.

The OSI bits/value may also be generated using hysteresis so that anindication of excessive interference does not toggle too frequently. Forexample, OSI bit 2 may be set to ‘1’ only if the measured interferenceexceeds the high threshold for a first time duration T_(W1) (e.g., 50milliseconds) and may be reset to ‘0’ only if the measured interferenceis below the high threshold for a second time duration T_(w2). Asanother example, OSI bit 2 may be set to ‘1’ only if the measuredinterference exceeds a first high threshold I_(high) _(—) _(th1) and maythereafter be reset to ‘0’ only if the measured interference falls belowa second high threshold I_(high) _(—) _(th2), where I_(high) _(—)_(th1)>I_(high) _(—) _(th2).

Sector m broadcasts its OTA OSI report, which may contain the two OSIbits or the tri-level OSI value, for user-based interference control.Sector m may broadcast the OTA OSI report in various manners. In anembodiment, sector m broadcasts the OTA OSI report in each measurementperiod. In another embodiment, sector m broadcasts OSI bit 1 in eachmeasurement period and broadcasts OSI bit 2 only if this bit is set to‘1’. Sector m may also broadcast OSI reports from other sectors to theterminals within sector m for better OSI coverage.

Sector m also sends its IS OSI report to the neighbor sectors fornetwork-based interference control. The IS OSI report may contain thetwo OSI bits, the tri-level OSI value, the measured interferencequantized to a predetermined number of bits, or some other information.Sector m may send the IS OSI report in each measurement period, or onlyif excessive interference is observed, or if some other criterion issatisfied. Another sector q may also request sector m to send IS OSIreport if the terminals in sector q indicate that they cannot receivethe OSI bits from sector m. Each sector uses the IS OSI reports from theneighbor sectors to control data transmissions from the terminals in itssector to mitigate inter-sector interference at the neighbor sectors.

Network-based interference control may be achieved in various manners.Some embodiments of network-based interference control are describedbelow.

In one embodiment, sector m schedules terminals in the sector based onthe IS OSI reports received from the neighbor sectors. For example, ifone or more neighbor sectors observe excessive interference, then sectorm may reduce the transmit powers used by disadvantaged terminals insector m so that these terminals cause less interference to othersectors. A disadvantaged terminal has a small channel gain (or a largepath loss) for the serving sector and needs to transmit at a high powerlevel in order to achieve a given signal-to-noise-and-interference ratio(SNR) at the serving sector. The disadvantaged terminal is typicallylocated closer to a neighbor sector, and the high transmit power levelresults in high inter-sector interference to this neighbor sector.

Sector m may identify disadvantaged terminals based on various qualitymetrics such as channel gain, pilot strength, carrier-to-noise ratio(C/N), channel gain ratio, and so on. These quality metrics may beestimated based on pilot and/or other transmissions sent by theterminals. For example, the estimated channel gain for a terminal may becompared against a channel gain threshold, and the terminal may bedeemed to be a disadvantaged terminal if its channel gain is below thechannel gain threshold. Sector m may reduce the transmit powers used bythe disadvantaged terminals by (1) lowering a high transmit power limitthat is applicable to the terminals, (2) lowering a lower transmit powerlimit that is applicable to the terminals, (3) assigning thedisadvantaged terminals with lower data rates that require lower SNRsand hence lower transmit powers, (4) not scheduling disadvantagedterminals for data transmission, or (5) using some other method orcombination of methods.

In another embodiment, sector m uses admission control to mitigateinter-sector interference observed by neighbor sectors. For example, ifone or more neighbor sectors observe excessive interference, then sectorm may reduce the number of active terminals in the sector by (1) denyingaccess to new terminals requesting to transmit on the reverse link, (2)denying access to disadvantaged terminals, (3) de-assigning terminalsthat have already been granted access, (4) de-assigning disadvantagedterminals, or (5) using some other admission control methods. The rateof de-assigning terminals may also be made a function of the IS OSIreports from the neighbor sectors (e.g., the observed interferencelevels), the number of neighbor sectors observing excessiveinterference, and/or other factors. Sector m may thus adjust the loadingof the sector based on the IS OSI reports from the neighbor sectors.

In yet another embodiment, sector m assigns traffic channels to theterminals in the sector in a manner to mitigate inter-sectorinterference observed by the neighbor sectors. For example, each sectormay be assigned a set of traffic channels that it may in turn assign tothe terminals in the sector. Neighboring sectors may also share a commonset of traffic channels that is orthogonal to the set of trafficchannels assigned to each sector. If one or more neighbor sectorsobserve excessive interference, then sector m may assign disadvantagedterminals in sector m with traffic channels in the common set. Thesedisadvantaged terminals would then cause no interference to the neighborsectors since the traffic channels in the common set are orthogonal tothe traffic channels assigned to the neighbor sectors. As anotherexample, each sector may be assigned a set of traffic channels that itmay assign to strong terminals that can tolerate high levels ofinterference. If one or more neighbor sectors observe excessiveinterference, then sector m may assign disadvantaged terminals in sectorm with traffic channels assigned to strong terminals in the neighborsectors.

For clarity, much of the description above is for one sector m. Eachsector in the system may perform interference control as described abovefor sector m.

User-based interference control may also be achieved in various manners.In an embodiment, user-based interference control is achieved byallowing the terminals to autonomously adjust their transmit powersbased on the OTA OSI reports received from the neighbor sectors.

FIG. 3 shows a process 300 performed by one terminal u for interferencecontrol. Terminal u receives an OTA OSI report from a neighbor sector(block 312). A determination is then made whether the neighbor sectorobserves excessive interference, e.g., whether OSI bit 2 is set to ‘1’(block 314). If the answer is ‘Yes’, then terminal u reduces itstransmit power with a larger down step size and/or at a faster rate(block 316). Otherwise, a determination is made whether the neighborsector observes high interference, e.g., whether OSI bit 1 is set to ‘1’and OSI bit 2 is set to ‘0’ (block 318). If the answer is ‘Yes’, thenterminal u reduces its transmit power with a nominal down step sizeand/or at a nominal rate (block 320). Otherwise, terminal u increasesits transmit power with a nominal up step size and/or at a nominal rate(block 322).

FIG. 3 shows an embodiment in which the OTA OSI report conveys theinter-sector interference observed by the neighbor sector in one ofthree possible levels—low, high, and excessive. Process 300 may beextended to cover any number of interference levels. In general, thetransmit power for terminal u may be (1) reduced by a down step that isrelated to the amount of interference observed by the neighbor sector(e.g., larger down step for higher interference) when the measuredinterference is above a given threshold and/or (2) increased by an upstep that is inversely related to the amount of interference observed bythe neighbor sector (e.g., larger up step for lower interference) whenthe measured interference is below the given threshold. The step sizeand/or the adjustment rate may also be determined based on otherparameters such as, for example, the current transmit power level forthe terminal, the channel gain for the neighbor sector relative to thechannel gain for the serving sector, prior OTA OSI reports, and so on.

Terminal u may adjust its transmit power based on the OTA OSI reportfrom one or multiple neighbor sectors. Terminal u may estimate thechannel gain for each sector based on a pilot received from the sector.Terminal u may then derive a channel gain ratio for each neighbor sectoras follows:

$\begin{matrix}{{{r_{i}(n)} = \frac{g_{{ns},i}(n)}{g_{ss}(n)}},} & {{Eq}\mspace{14mu} (9)}\end{matrix}$

where

-   -   g_(ns,i)(n) is the channel gain between terminal u and neighbor        sector i;    -   g_(ss)(n) is the channel gain between terminal u and the serving        sector; and    -   r_(i)(n) is the channel gain ratio for neighbor sector i.

In one embodiment, terminal u identifies the strongest neighbor sectorwith the largest channel gain ratio. Terminal u then adjusts itstransmit power based on the OTA OSI report from only this strongestneighbor sector. In another embodiment, terminal u adjusts its transmitpower based on the OTA OSI reports from all sectors in an OSI set. ThisOSI set may contain (1) T strongest neighbor sectors, where T≧1, (2)neighbor sectors with channel gain ratios exceeding a channel gain ratiothreshold, (3) neighbor sectors with channel gains exceeding a channelgain threshold, (4) neighbor sectors included in a neighbor listbroadcast by the serving sector, or (5) some other group of neighborsectors. Terminal u may adjust its transmit power in various mannersbased on the OTA OSI reports from multiple neighbor sectors in the OSIset. For example, terminal u may decrease its transmit power if anyneighbor sector in the OSI set observes high or excessive interference.As another example, terminal u may determine a transmit power adjustmentfor each neighbor sector in the OSI set and may then combine theadjustments for all neighbor sectors in the OSI set to obtain an overalltransmit power adjustment.

In general, transmit power adjustment for interference control may beperformed in conjunction with various power control schemes. Forclarity, a specific power control scheme is described below. For thispower control scheme, the transmit power for a traffic channel assignedto terminal u may be expressed as:

P _(dch)(n)=P _(ref)(n)+ΔP(n),  Eq (10)

where

-   -   P_(dch)(n) is the transmit power for the traffic channel for        update interval n;    -   P_(ref)(n) is a reference power level for update interval n; and    -   ΔP(n) is a transmit power delta for update interval n.        The transmit power levels P_(dch)(n) and P_(ref)(n) and the        transmit power delta ΔP(n) are given in units of decibels (dB).

The reference power level P_(ref)(n) is the amount of transmit powerneeded to achieve a target SNR for a designated transmission, which maybe signaling sent by terminal u on a control channel or some othertransmission. The reference power level and the target SNR may beadjusted to achieve a desired level of performance for the designatedtransmission, e.g., 1% packet error rate (PER). If the data transmissionon the traffic channel and the designated transmission observe similarnoise and interference characteristics, then the received SNR for thedata transmission, SNR_(dch)(n), may be estimated as:

SNR _(dch)(n)=SNR _(target) +ΔP(n).  Eq (11)

The transmit power delta ΔP(n) may be adjusted in a deterministicmanner, a probabilistic manner, or some other manner based on the OTAOSI reports from the neighbor sectors. The transmit power may beadjusted (1) by different amounts for different interference levelsusing deterministic adjustment or (2) at different rates for differentinterference levels using probabilistic adjustment. Exemplarydeterministic and probabilistic transmit power adjustment schemes aredescribed below. For simplicity, the following description is fortransmit power adjustment for an OSI bit received from one neighborsector. This OSI bit may be OSI bit 1 or 2.

FIG. 4 shows a process 400 for adjusting the transmit power of terminalu in a deterministic manner. Initially, terminal u processes an OTA OSIreport from a neighbor sector (block 412) and determines whether the OSIbit is ‘1’ or ‘0’ (block 414). If the OSI bit is ‘1’, which indicatesthat the observed interference exceeds an interference threshold, thenterminal u determines the amount of reduction in transmit power, or adown step size ΔP_(dn)(n) (block 422). ΔP_(dn)(n) may be determinedbased on the transmit power delta for the prior update interval,ΔP(n−1), and a channel gain ratio for the neighbor sector, r_(ns)(n).Terminal u then decreases the transmit power delta by ΔP_(dn)(n) (block424). Conversely, if the OSI bit is ‘0’, then terminal u determines theamount of increase in transmit power, or an up step size ΔP_(P)(n)(block 432). ΔP_(up)(n) may also be determined based on ΔP(n−1) andr_(ns)(n). Terminal u then increases the transmit power delta byΔP_(up)(n) (block 434). The transmit power adjustments in blocks 424 and434 may be expressed as:

$\begin{matrix}{{\Delta \; {P(n)}} = \{ \begin{matrix}{{{\Delta \; {P( {n - 1} )}} + {\Delta \; {P_{up}(n)}}},} & {{{{if}\mspace{14mu} {OSI}\mspace{14mu} {bit}} = {{}_{}^{}{}_{}^{}}},{and}} \\{{{\Delta \; {P( {n - 1} )}} - {\Delta \; {P_{dn}(n)}}},} & {{{if}\mspace{14mu} {OSI}\mspace{14mu} {bit}} = {{{}_{}^{}{}_{}^{}}.}}\end{matrix} } & {{Eq}\mspace{14mu} (12)}\end{matrix}$

After blocks 424 and 434, terminal u limits the transmit power deltaΔP(n) to be within a range of allowable transmit power deltas (block442), as follows:

ΔP(n)ε[ΔP _(min) ,ΔP _(min)],  Eq (13)

where ΔP_(min) is the minimum transmit power delta allowable for thetraffic channel, and

-   -   ΔP_(max) is the maximum transmit power delta allowable for the        traffic channel.        Constraining the transmit power deltas for all terminals in a        sector to within a range of transmit power deltas, as shown in        equation (13), can maintain the intra-sector interference within        acceptable levels. The minimum transmit power delta ΔP_(min) may        be adjusted by a control loop to ensure that each terminal can        meet the requirements for a quality of service (QoS) class to        which the terminal belongs. ΔP_(min) for different QoS classes        may be adjusted at different rates and/or with different step        sizes.

Terminal u then computes the transmit power P_(dch)(n) for the trafficchannel based on the transmit power delta ΔP(n) and the reference powerlevel P_(ref)(n), as shown in equation (10) (block 444). Terminal u maylimit the transmit power P_(dch)(n) to be within the maximum power levelP_(max) (block 446), as follows:

$\begin{matrix}{{P_{dch}(n)} = \{ \begin{matrix}{{P_{dch}(n)},} & {{{{if}\mspace{14mu} {P_{dch}(n)}} \leq P_{\max}},} \\{P_{\max},} & {{otherwise}.}\end{matrix} } & {{Eq}\mspace{14mu} (14)}\end{matrix}$

Terminal u uses the transmit power P_(dch)(n) for data transmission onthe traffic channel.

In an embodiment, the ΔP_(dn)(n) and ΔP_(up)(n) step sizes are computedas:

ΔP _(dn)(n)=ƒ_(dn)(ΔP _(dn,min) ,ΔP(n−1),r _(ns)(n),k _(dn)),  Eq (15a)

and

ΔP _(up)(n)=ƒ_(up)(ΔP _(up,min) ,ΔP(n−1),r _(ns)(n),k _(up)),  Eq (15b)

where

-   -   ΔP_(dn,min) and ΔP_(up,min) are minimum values for ΔP_(dn)(n)        and ΔP_(up)(n), respectively;    -   k_(dn) and k_(up) are scaling factors for ΔP_(dn)(n) and        ΔP_(up)(n), respectively; and    -   ƒ_(dn)( ) and ƒ_(up)( ) are functions to compute Δp_(dn)(n) and        ΔP_(up)(n) respectively.

Function ƒ_(dn)( ) may be defined such that ΔP_(dn)(n) is related toboth ΔP(n−1) and r_(ns)(n). If a neighbor sector observes high orexcessive interference, then (1) a larger channel gain for the neighborsector results in a larger ΔP_(dn)(n) and (2) a larger value of ΔP(n−1)results in a larger ΔP_(dn)(n). Function ƒ_(up) ( ) may be defined suchthat ΔP_(P)(n) is inversely related to both ΔP(n−1) and r_(ns)(n). Ifthe neighbor sector observes low interference, then (1) a larger channelgain for the neighbor sector results in a smaller ΔP_(up)(n) and (2) alarger value of ΔP(n−1) results in a smaller ΔP_(up)(n).

FIG. 4 shows the processing for one OSI bit from one neighbor sector. Alarger value may be used for ΔP_(dn)(n) when the neighbor sectorobserves excessive interference. A smaller value may be used forΔP_(dn)(n) when the neighbor sector observes high interference.Different down step sizes may be obtained, e.g., by using differentscaling factors k_(dn1) and k_(dn2) for high and excessive interference,respectively.

FIG. 5 shows a process 500 for adjusting the transmit power of terminalu in a probabilistic manner. Initially, terminal u processes an OTA OSIreport from a neighbor sector (block 512) and determines whether the OSIbit is ‘1’ or ‘0’ (block 514). If the OSI bit is ‘1’, then terminal udetermines the probability for decreasing the transmit power,Pr_(dn)(n), e.g., based on ΔP(n−1) and r_(ns)(n) (block 522). Terminal uthen randomly selects a value x between 0.0 and 1.0, where x is a randomvariable uniformly distributed between 0.0 and 1.0 (block 524). If x isless than or equal to Pr_(dn)(n), as determined in block 526, thenterminal u decreases its transmit power delta by ΔP_(du) (block 528).Otherwise, if x is greater than Pr_(dn)(n), then terminal u maintainsthe transmit power delta at the current level (block 530).

If the OSI bit is ‘0’ in block 514, then terminal u determines theprobability for increasing the transmit power, Pr_(up)(n), e.g., basedon ΔP(n−1) and r_(ns)(n) (block 532). Terminal u then randomly selects avalue x between 0.0 and 1.0 (block 534). If x is less than or equal toPr_(up)(n), as determined in block 536, then terminal u increases itstransmit power delta by ΔP_(P) (block 538). Otherwise, if x is greaterthan Pr_(up)(n), then terminal u maintains the transmit power delta atthe current level (block 530). The transmit power adjustments in blocks528, 530, and 538 may be expressed as:

$\begin{matrix}{{\Delta \; {P(n)}} = \{ \begin{matrix}{{{\Delta \; {P( {n - 1} )}} - {\Delta \; P_{dn}}},} & {{{{if}\mspace{14mu} {OSI}\mspace{14mu} {bit}} = {{{{}_{}^{}{}_{}^{}}\mspace{14mu} {AND}\mspace{14mu} x} \leq {\Pr_{dn}(n)}}},} \\{{{\Delta \; {P( {n - 1} )}} + {\Delta \; P_{up}}},} & {{{{if}\mspace{14mu} {OSI}\mspace{14mu} {bit}} = {{{{}_{}^{}{}_{}^{}}\mspace{14mu} {AND}\mspace{14mu} x} \leq {\Pr_{up}(n)}}},} \\{{\Delta \; {P( {n - 1} )}},} & {{otherwise}.}\end{matrix} } & {{Eq}\mspace{14mu} (16)}\end{matrix}$

ΔP_(du) and ΔP_(up) may be the same value (e.g., 0.25 dB, 0.5 dB, 1.0dB, and so on) or may be different values.

After blocks 528, 530, and 538, terminal u limits the transmit powerdelta, as shown in equation (13) (block 542). Terminal u then computesthe transmit power P_(dch)(n) based on the transmit power delta ΔP(n)and the reference power level P_(ref)(n), as shown in equation (10)(block 544), and further limits the transmit power P_(dch)(n) to bewithin the maximum power level, as shown in equation (14) (block 546).Terminal u uses the transmit power P_(dch)(n) for data transmission onthe traffic channel.

In an embodiment, the probabilities are computed as follows:

Pr _(dn)(n)=ƒ′_(dn)(Pr _(dn,min) ,ΔP(n−1),r _(ns)(n),k _(dn)),  Eq (17a)

and

Pr _(up)(n)=ƒ′_(up)(Pr _(up,min) ,ΔP(n−1),r _(ns)(n),k _(up)),  Eq (17b)

where Pr_(dn,min) and Pr_(up,min) are minimum values for Pr_(dn)(n) andPr_(up)(n), respectively; and ƒ′_(dn)( ) and ƒ′_(up)( ) are functions tocompute Pr_(dn)(n) and Pr_(up)(n), respectively.

Function ƒ′_(dn)( ) may be defined such that Pr_(dn)(n) is related toboth ΔP(n−1) and r_(ns)(n). If a neighbor sector observes high orexcessive interference, then (1) a larger channel gain for the neighborsector results in a larger Pr_(dn)(n) and (2) a larger value of ΔP(n−1)results in a larger Pr_(dn)(n). The larger Pr_(dn)(n) results in ahigher probability of reducing the transmit power. Function ƒ′_(up)( )may be defined such that Pr_(up)(n) is inversely related to both ΔP(n−1)and r_(ns)(n). If the neighbor sector observes low interference, then(1) a larger channel gain for the neighbor sector results in a smallerPr_(up)(n) and (2) a larger value of ΔP(n−1) results in a smallerPr_(up)(n). The smaller Pr_(up)(n) results in a lower probability ofincreasing the transmit power.

FIG. 5 shows the processing for one OSI bit from one neighbor sector. Alarger value may be used for Pr_(dn)(n) when the neighbor sectorobserves excessive interference. A smaller value may be used forPr_(dn)(n) when the neighbor sector observes high interference.Different down probabilities and hence different rates of poweradjustment may be obtained, e.g., by using different scaling factorsk_(dn1) and k_(dn2) for high and excessive interference, respectively.

In general, various functions may be used to compute the ΔP_(dn)(n) andΔP_(up)(n) step sizes and the Pr_(dn)(n) and Pr_(up)(n) probabilities. Afunction may be defined based on various parameters such as the currenttransmit power, the current transmit power delta, the current OTA OSIreport, previous OTA OSI reports, channel gains, and so on. Eachfunction may have a different impact on various power controlcharacteristics such as the convergence rate of the transmit poweradjustment and the distribution of transmit power deltas for theterminals in the system. The step sizes and probabilities may also bedetermined based on look-up tables or by some other means.

The transmit power adjustment and/or the admission control describedabove may also be performed based on QoS class, user priority class, andso on. For example, a terminal using an emergency service and a policeterminal may have higher priority and may be able adjust transmit powerat a faster rate and/or with larger step sizes than a normal priorityuser. As another example, a terminal sending voice traffic may adjusttransmit power at a slower rate and/or with smaller step sizes.

Terminal u may also vary the manner in which the transmit power isadjusted based on prior OTA OSI reports received from neighbor sectors.For example, terminal u may reduce its transmit power by a particulardown step size and/or at a particular rate if a neighbor sector reportsexcessive interference and may reduce the transmit power by a largerdown step size and/or at a faster rate if the neighbor sector continuesto report excessive interference. Alternatively or additionally,terminal u may ignore the ΔP_(min) in equation (13) if a neighbor sectorreports excessive interference, or if the neighbor sector continues toreport excessive interference.

Various embodiments of power control to mitigate inter-sectorinterference have been described above. Interference and power controlmay also be performed in other manners, and this is within the scope ofthe invention.

In an embodiment, each sector broadcasts its OTA OSI report to theterminals in the neighbor sectors, as described above. The OTA OSIreport may be broadcast with sufficient transmit power to achieve thedesired coverage in the neighbor sectors. Each terminal may receive theOTA OSI reports from the neighbor sectors and process these OTA OSIreports in a manner to achieve a sufficiently low misdetection rate anda sufficiently low false alarm probability. Misdetection refers to afailure to detect an OSI bit or value that has been transmitted. Falsealarm refers to erroneous detection of a received OSI bit or value. Forexample, if an OSI bit is transmitted using BPSK, then a terminal maydeclare a received OSI bit to be (1) a ‘0’ if the detected OSI bit isbelow a first threshold, OSI bit<-B_(th), (2) a ‘1’ if the detected OSIbit exceeds a second threshold, OSI bit>+B_(th), and (3) a null bitotherwise, +B_(th)≦OSI bit≦−B_(th). The terminal can typically trade offmisdetection rate with false alarm probability by adjusting thethresholds used for detection.

In another embodiment, each sector also broadcasts OTA OSI reportsgenerated by the neighbor sectors to the terminals within its sector.Each sector thus acts a proxy for neighbor sectors. This embodiment canensure that each terminal can reliably receive the OTA OSI reportsgenerated by the neighbor sectors since the terminal can receive theseOTA OSI reports from the serving sector. This embodiment is well suitedfor an asymmetric network deployment in which sector coverage sizes arenot equal. Smaller sectors typically transmit at lower power levels, andthe OTA OSI reports broadcast by these smaller sectors may not bereliably received by the terminals in the neighbor sectors. The smallersectors would then benefit from having their OTA OSI reports broadcastby the neighbor sectors.

In general, a given sector m may broadcast OTA OSI reports generated byany number and any one of the other sectors. In an embodiment, sector mbroadcasts OTA OSI reports generated by sectors in a neighbor list forsector m. The neighbor list may be formed by a network operator or insome other manner. In another embodiment, sector m broadcasts OTA OSIreports generated by all sectors that are included in the active sets ofthe terminals in sector m. Each terminal may maintain an active set thatincludes all sectors with which the terminal is in communication.Sectors may be added to or removed from the active set as the terminalis handed off from one sector to another. In yet another embodiment,sector m broadcasts OTA OSI reports generated by all sectors that areincluded in the candidate sets of the terminals in sector m. Eachterminal may maintain a candidate set that includes all sectors withwhich the terminal may communicate. Sectors may be added to or removedfrom the candidate set, e.g., based on channel gain and/or some otherparameter. In yet another embodiment, sector m broadcasts OTA OSIreports generated by all sectors that are included in the OSI sets ofthe terminals in sector m. The OSI set for each terminal may be definedas described above.

As noted above, the system may utilize only user-based interferencecontrol or only network-based interference control. User-basedinterference control may be simpler to implement since each sector andeach terminal can act autonomously. Network-based interference controlmay provide improved performance since interference control is performedin a coordinated manner. The system may also utilize both user-based andnetwork-based interference control at the same time. The system may alsoutilize user-based interference control at all times and may invokenetwork-based interference control only if excessive interference isobserved. The system may also invoke each type of interference controlfor different operating conditions.

FIG. 6 shows a power control mechanism 600 that may be used to adjustthe transmit power for a terminal 120 x in system 100. Terminal 120 xcommunicates with a serving sector 110 x and may cause interference toneighbor sectors 110 a through 1101. Power control mechanism 600includes (1) a reference loop 610 that operates between terminal 120 xand serving sector 110 x and (2) a second loop 620 that operates betweenterminal 120 x and neighbor sectors 110 a through 1101. Reference loop610 and second loop 620 may operate concurrently but may be updated atdifferent rates, with reference loop 610 being a faster loop than secondloop 620. For simplicity, FIG. 6 shows only the portion of loops 610 and620 residing at terminal 120 x.

Reference loop 610 adjusts the reference power level P_(ref)(n) suchthat the received SNR for the designated transmission, as measured atserving sector 110 x, is as close as possible to the target SNR. Forreference loop 610, serving sector 110 x estimates the received SNR forthe designated transmission, compares the received SNR against thetarget SNR, and generates transmit power control (TPC) commands based onthe comparison results. Each TPC command may be either (1) an UP commandto direct an increase in the reference power level or (2) a DOWN commandto direct a decrease in the reference power level. Serving sector 110 xtransmits the TPC commands on the forward link (cloud 670) to terminal120 x.

At terminal 120 x, a TPC command processor 642 detects the TPC commandstransmitted by serving sector 110 x and provides TPC decisions. Each TPCdecision may be an UP decision if a received TPC command is deemed to bean UP command or a DOWN decision if the received TPC command is deemedto be an DOWN command. A reference power adjustment unit 644 adjusts thereference power level based on the TPC decisions. Unit 644 may increaseP_(ref)(n) by an up step for each UP decision and decrease P_(ref)(n) bya down step for each DOWN decision. A transmit (TX) data processor 660scales the designated transmission to achieve the reference power level.Terminal 120 x sends the designated transmission to serving sector 110x.

Due to path loss, fading, and multipath effects on the reverse link(cloud 640), which typically vary over time and especially for a mobileterminal, the received SNR for the designated transmission continuallyfluctuates. Reference loop 610 attempts to maintain the received SNR forthe designated transmission at or near the target SNR in the presence ofchanges in the reverse link channel conditions.

Second loop 620 adjusts the transmit power P_(dch)(n) for a trafficchannel assigned to terminal 120 x such that a power level that is ashigh as possible is used for the traffic channel while keepinginter-sector interference to within acceptable levels. For second loop620, each neighbor sector 110 receives transmissions on the reverselink, estimates the inter-sector interference observed by the neighborsector from the terminals in other sectors, generates an OTA OSI reportbased on the interference estimate, and broadcasts the OTA OSI report tothe terminals in the other sectors.

At terminal 120 x, an OSI report processor 652 receives the OTA OSIreports broadcast by the neighbor sectors and provides detected OSIreports to a transmit power delta computation unit 656. A channelestimator 654 receives pilots from the serving and neighbor sectors,estimates the channel gain for each sector, and provides the estimatedchannel gains for all sectors to unit 656. Unit 656 determines thechannel gain ratios for the neighbor sectors and further adjusts thetransmit power delta ΔP(n) based on the detected OSI reports and thechannel gain ratios, as described above. Unit 656 may implementprocesses 300, 400 and/or 500 shown in FIGS. 3 through 5. A transmitpower computation unit 658 computes the transmit power P_(dch)(n) basedon the reference transmit level P_(ref)(n) from unit 644, the transmitpower delta ΔP(n) from unit 656, and possibly other factors. TX dataprocessor 660 uses the transmit power P_(dch)(n) for data transmissionto serving sector 110 x.

FIG. 6 shows an exemplary power control mechanism that may be used forinterference control. Interference control may also be performed inother manners and/or with different parameters than those describedabove.

FIG. 7 shows a block diagram of an embodiment of terminal 120 x, servingbase station 110 x, and neighbor base station 110 y. For clarity, thefollowing description assumes the use of power control mechanism 600shown in FIG. 6.

On the reverse link, at terminal 120 x, a TX data processor 710 encodes,interleaves, and symbol maps reverse link (RL) traffic data and controldata and provides data symbols. A modulator (Mod) 712 maps the datasymbols and pilot symbols onto the proper subbands and symbol periods,performs OFDM modulation if applicable, and provides a sequence ofcomplex-valued chips. A transmitter unit (TMTR) 714 conditions (e.g.,converts to analog, amplifies, filters, and frequency upconverts) thesequence of chips and generates a reverse link signal, which istransmitted via an antenna 716.

At serving base station 110 x, multiple antennas 752 xa through 752 xtreceive the reverse link signals from terminal 120 x and otherterminals. Each antenna 752 x provides a received signal to a respectivereceiver unit (RCVR) 754 x. Each receiver unit 754 x conditions (e.g.,filters, amplifies, frequency downconverts, and digitizes) its receivedsignal, performs OFDM demodulation if applicable, and provides receivedsymbols. An RX spatial processor 758 performs receiver spatialprocessing on the received symbols from all receiver units and providesdata symbol estimates, which are estimates of the transmitted datasymbols. An RX data processor 760 x demaps, deinterleaves, and decodesthe data symbol estimates and provides decoded data for terminal 120 xand other terminals currently served by base station 110 x.

The processing for a forward link transmission may be performedsimilarly to that described above for the reverse link. The processingfor the transmissions on the forward and reverse links is typicallyspecified by the system.

For interference and power control, at serving base station 110 x, RXspatial processor 758 x estimates the received SNR for terminal 120 x,estimates the inter-sector interference observed by base station 110 x,and provides an SNR estimate for terminal 110 x and an interferenceestimate (e.g., the measured interference I_(meas,m)) to a controller770 x. Controller 770 x generates TPC commands for terminal 120 x basedon the SNR estimate for the terminal and the target SNR. Controller 770x may generate an OTA OSI report and/or an IS OSI report based on theinterference estimate. Controller 770 x may also receive IS OSI reportsfrom neighbor sectors via a communication (Comm) unit 774 x. The TPCcommands, the OTA OSI report for base station 110 x, and possibly OTAOSI reports for other sectors are processed by a TX data processor 782 xand a TX spatial processor 784 x, conditioned by transmitter units 754xa through 754 xt, and transmitted via antennas 752 xa through 752 xt.The IS OSI report from base station 110 x may be sent to the neighborsectors via communication unit 774 x.

At neighbor base station 110 y, an RX spatial processor 758 y estimatesthe inter-sector interference observed by base station 110 y andprovides an interference estimate to controller 770 y. Controller 770 ymay generate an OTA OSI report and/or an IS OSI report based on theinterference estimate. The OTA OSI report is processed and broadcast tothe terminals in the system. The IS OSI report may be sent to theneighbor sectors via a communication unit 774 y.

At terminal 120 x, antenna 716 receives the forward link signals fromthe serving and neighbor base stations and provides a received signal toa receiver unit 714. The received signal is conditioned and digitized byreceiver unit 714 and further processed by a demodulator (Demod) 742 andan RX data processor 744. Processor 744 provides the TPC commands sentby serving base station 110 x for terminal 120 x and the OTA OSI reportsbroadcast by the neighbor base stations. A channel estimator withindemodulator 742 estimates the channel gain for each base station.Controller 720 detects the received TPC commands and updates thereference power level based on the TPC decisions. Controller 720 alsoadjusts the transmit power for the traffic channel based on the OTA OSIreports received from the neighbor base stations and the channel gainsfor the serving and neighbor base stations. Controller 720 provides thetransmit power for the traffic channel assigned to terminal 120 x.Processor 710 and/or modulator 712 scales the data symbols based on thetransmit power provided by controller 720.

Controllers 720, 770 x, and 770 y direct the operations of variousprocessing units at terminal 120 x and base station 110 x and 110 y,respectively. These controllers may also perform various functions forinterference and power control. For example, controller 720 mayimplement any or all of units 642 through 658 shown in FIG. 6 and/orprocesses 300, 400 and/or 500 shown in FIGS. 3 through 5. Controller 770for each base station 110 may implement all or a portion of process 200in FIG. 2. Memory units 722, 772 x, and 772 y store data and programcodes for controllers 720, 770 x, and 770 y, respectively. A scheduler780 x schedules terminals for communication with base station 110 x andalso assigns traffic channels to the scheduled terminals, e.g., based onthe IS OSI reports from the neighbor base stations.

The interference control techniques described herein may be implementedby various means. For example, these techniques may be implemented inhardware, software, or a combination thereof. For a hardwareimplementation, the processing units used to perform interferencecontrol at a base station may be implemented within one or moreapplication specific integrated circuits (ASICs), digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, micro-controllers, microprocessors,electronic devices, other electronic units designed to perform thefunctions described herein, or a combination thereof. The processingunits used to perform interference control at a terminal may also beimplemented within one or more ASICs, DSPs, processors, electronicdevices, and so on.

For a software implementation, the interference control techniques maybe implemented with modules (e.g., procedures, functions, and so on)that perform the functions described herein. The software codes may bestored in a memory unit (e.g., memory unit 722, 772 x, or 772 y in FIG.7) and executed by a processor (e.g., controller 720, 770 x, or 770 y).The memory unit may be implemented within the processor or external tothe processor.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. A method for interference control, the method being implemented by asector, the method comprising: obtaining a measured interference thatrepresents an estimate of interference observed at the sector due totransmissions from terminals in other sectors; generating aninterference report based on the measured interference; and broadcastingthe interference report to the terminals in the other sectors.
 2. Themethod of claim 1, wherein the interference report indicates whether themeasured interference is greater than or less than an interferencethreshold.
 3. The method of claim 1, wherein the interference reportconveys the measured interference relative to multiple interferencethresholds.
 4. The method of claim 1, wherein the measured interferenceis a measured interference-over-thermal.
 5. The method of claim 1,further comprising broadcasting interference reports received from othersectors to terminals being served by the sector.
 6. A method forinterference control, the method being implemented by a terminal, themethod comprising: receiving an interference report that is broadcast bya neighbor sector; and adjusting transmit power of the terminal based onthe interference report.
 7. The method of claim 6, further comprising:receiving multiple interference reports from multiple neighbor sectors;and identifying a strongest neighbor sector; wherein the transmit powerof the terminal is adjusted based only on the interference report fromthe strongest neighbor sector.
 8. The method of claim 6, furthercomprising receiving multiple interference reports from multipleneighbor sectors, wherein the transmit power of the terminal is adjustedbased only on the interference reports from the neighbor sectors thatare included in an other-sector interference set.
 9. The method of claim8, wherein adjusting the transmit power comprises decreasing thetransmit power if any neighbor sector in the other-sector interferenceset observes high or excessive interference.
 10. The method of claim 8,wherein adjusting the transmit power comprises: determining a transmitpower adjustment for each neighbor sector in the other-sectorinterference set; and combining transmit power adjustments for allneighbor sectors in the other-sector interference set to obtain anoverall transmit power adjustment.
 11. A sector that is configured forinterference control, comprising: a processor; memory in electroniccommunication with the processor; and instructions stored in the memory,the instructions being executable to: obtain a measured interferencethat represents an estimate of interference observed at the sector dueto transmissions from terminals in other sectors; generate aninterference report based on the measured interference; and broadcastthe interference report to the terminals in the other sectors.
 12. Thesector of claim 11, wherein the interference report indicates whetherthe measured interference is greater than or less than an interferencethreshold.
 13. The sector of claim 11, wherein the interference reportconveys the measured interference relative to multiple interferencethresholds.
 14. The sector of claim 11, wherein the measuredinterference is a measured interference-over-thermal.
 15. The sector ofclaim 11, wherein the instructions are also executable to broadcastinterference reports received from other sectors to terminals beingserved by the sector.
 16. A terminal configured for interferencecontrol, comprising: a processor; memory in electronic communicationwith the processor; and instructions stored in the memory, theinstructions being executable to: receive an interference report that isbroadcast by a neighbor sector; and adjust transmit power of theterminal based on the interference report.
 17. The terminal of claim 16,wherein the instructions are also executable to receive multipleinterference reports from multiple neighbor sectors and to identify astrongest neighbor sector, wherein the transmit power of the terminal isadjusted based only on the interference report from the strongestneighbor sector.
 18. The terminal of claim 16, wherein the instructionsare also executable to receive multiple interference reports frommultiple neighbor sectors, and wherein the transmit power of theterminal is adjusted based only on the interference reports from theneighbor sectors that are included in an other-sector interference set.19. The terminal of claim 18, wherein adjusting the transmit powercomprises decreasing the transmit power if any neighbor sector in theother-sector interference set observes high or excessive interference.20. The terminal of claim 18, wherein adjusting the transmit powercomprises: determining a transmit power adjustment for each neighborsector in the other-sector interference set; and combining transmitpower adjustments for all neighbor sectors in the other-sectorinterference set to obtain an overall transmit power adjustment.
 21. Asector that is configured for interference control, comprising: meansfor obtaining a measured interference that represents an estimate ofinterference observed at the sector due to transmissions from terminalsin other sectors; means for generating an interference report based onthe measured interference; and means for broadcasting the interferencereport to the terminals in the other sectors.
 22. The sector of claim21, wherein the interference report indicates whether the measuredinterference is greater than or less than an interference threshold. 23.The sector of claim 21, wherein the interference report conveys themeasured interference relative to multiple interference thresholds. 24.A terminal that is configured for interference control, comprising:means for receiving an interference report that is broadcast by aneighbor sector; and means for adjusting transmit power of the terminalbased on the interference report.
 25. The terminal of claim 24, furthercomprising: means for receiving multiple interference reports frommultiple neighbor sectors; and means for identifying a strongestneighbor sector; wherein the transmit power of the terminal is adjustedbased only on the interference report from the strongest neighborsector.
 26. The terminal of claim 24, further comprising means forreceiving multiple interference reports from multiple neighbor sectors,wherein the transmit power of the terminal is adjusted based only on theinterference reports from the neighbor sectors that are included in another-sector interference set.
 27. A non-transitory processor-readablestorage medium, comprising: code for causing a sector to obtain ameasured interference that represents an estimate of interferenceobserved at the sector due to transmissions from terminals in othersectors; code for causing the sector to generate an interference reportbased on the measured interference; and code for causing the sector tobroadcast the interference report to the terminals in the other sectors.28. The processor-readable storage medium of claim 27, wherein theinterference report indicates whether the measured interference isgreater than or less than an interference threshold.
 29. Theprocessor-readable storage medium of claim 27, wherein the interferencereport conveys the measured interference relative to multipleinterference thresholds.
 30. A non-transitory processor-readable storagemedium, comprising: code for causing a terminal to receive aninterference report that is broadcast by a neighbor sector; and code forcausing the terminal to adjust transmit power of the terminal based onthe interference report.
 31. The processor-readable storage medium ofclaim 30, further comprising: code for causing the terminal to receivemultiple interference reports from multiple neighbor sectors; and codefor causing the terminal to identify a strongest neighbor sector;wherein the transmit power of the terminal is adjusted based only on theinterference report from the strongest neighbor sector.
 32. Theprocessor-readable storage medium of claim 30, further comprising codefor causing the terminal to receive multiple interference reports frommultiple neighbor sectors, wherein the transmit power of the terminal isadjusted based only on the interference reports from the neighborsectors that are included in an other-sector interference set.